Browsing by Author "Zhai, Tianyou"

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Bio-Inspired Flexible Fluoropolymer Film for All-Mode Light Extraction Enhancement
(2019-05-29)
Liang, Renli
;
Hu, Run
;
Long, Hanling
;
Huang, Xinyu
;
Dai, Jiangnan
Enhancing the light extraction efficiency is a prevalent but vital challenge for most solid-state lighting technologies, especially for deep ultraviolet light-emitting diodes (DUV-LEDs). In this paper, inspired by the micro-structure of the butterfly's eye, we propose and fabricate a flexible fluoropolymer film (FFP film) to tackle this issue for all-mode, full-wavelength light extraction enhancement for most solid-state lighting technologies compatibly. The experimental results demonstrate that compared with one mounted with a smooth FFP film, the light output power of DUV-LED is enhanced up to 26.7% by mounting the FFP film with 325 nm radius nanocones at a driving current of 200 mA. Importantly, thanks to the super-flexible feature of the FFP film, it can both cover the top surface and sidewalls of the DUV-LED chip, leading to the improvement of transverse electric and transverse magnetic mode light extraction by 20.5 and 21.8%, respectively. Finite element analysis (FEA) simulations of the electric field distribution of DUV-LEDs with the FFP film reveal the underlying physics. The present strategy is proposed from the view of the packaging level, which is cost-effective, able to be manufactured at a large scale, and compatible with the solid-state lighting technologies.
Layer-Dependent Dielectric Function of Wafer-Scale 2D MoS2
(2019-01-18)
Song, Baokun
;
Gu, Honggang
;
Fang, Mingsheng
;
Chen, Xiuguo
;
Jiang, Hao
Wafer-scale, high-quality, and layer-controlled 2D MoS2 films on c-sapphire are synthesized by an innovative two-step method. The dielectric functions of MoS2 ranging from the monolayer to the bulk are investigated by spectroscopic ellipsometry over an ultra-broadband (0.73-6.42 eV). Up to five critical points (CPs) in the dielectric function spectra are precisely distinguished by CP analysis, and their physical origins are identified in the band structures with the help of first-principles calculations. Results demonstrate that the center energies of these CPs exhibit intriguing layer dependency, which are interpreted by the intrinsic layer-dependent transitions in MoS2. Specially, the change in the imaginary part of the dielectric functions versus the thickness exhibits a "W" like curve, and the two valley bottoms appear at about four-layer and 10-layer respectively. These complex fluctuations are attributed to the alternating domination of the decreasing excitonic effect, the increasing joint density of states, and the mass density increase in relative thick MoS2 samples.